1. Field of the Invention
The present invention relates in general to a vibration damping device adapted to be interposed between components to be linked in a vibration damped manner in order to provide vibration damped linkage or vibration damped support of these components, wherein the vibration damping device is a fluid filled vibration damping device that utilizes vibration damping action based on the flow action of a fluid filling the interior. The invention relates in particular to a fluid filled vibration damping device in which a fluid passage interconnecting a fluid filled pressure receiving chamber and equilibrium chamber is switchable between a communicating state and a blocked state.
2. Description of the Related Art
There are any number of known vibration damping devices proposed to date as devices for interposition between components that make up a vibration transmission system in order to provide vibration damped linkage or vibration damped support of the components to one another. One type of vibration damping device is a fluid filled vibration damping device having a construction provided in its interior with a pressure receiving chamber and an equilibrium chamber filled with a non-compressible fluid, which chambers communicate through a fluid passage. Such devices have been employed as automotive engine mounts or sub-frame mounts, for example.
With certain fluid filled vibration damping devices, switching control of vibration damping characteristics is possible where the fluid passage interconnecting the pressure receiving chamber and the equilibrium chamber is switchable between a communicating state and a blocked state by a movable valve body that is driven by pneumatic pressure or electromagnetic force. As one example, Japanese Unexamined Patent Publication No. JP-A-2004-150546 teaches a fluid filled vibration damping device having a construction in which a mover composed of a ferroelectric body undergoes actuated displacement under the action of a magnetic field that is produced by a stator having a coil, whereby the fluid passage can be switched between the communicating state and the blocked state by a movable valve body that is constituted by the mover.
Accordingly, in order to maintain the mover in the displaced state with respect to the stator in JP-A-2004-150546, it will be necessary to maintain energization of the coil so that retention force continues to act on the mover. However, maintaining continuous energization of the coil not only increases the amount of power consumed, but also poses a problem of diminished durability owing to high heat emission by the coil.
There has also been proposed a structure, shown in JP-A-2004-150546 as well, whereby a coil spring is employed to provide constant urging force that acts on the mover towards one side in the actuation direction, whereby the coil will be energized when the mover is to be actuated in the opposite direction from the urging direction, whereas energization will be needed when the mover is to be actuated in the urging direction.
However, such a construction utilizing the urging force of a coil spring will require to provide a coil spring as an additional separate component. This results in a number of drawbacks such as a greater number of parts and a commensurately more complicated structure, as well as lower productivity owing to the need for a coil spring assembly step.